Multicolor, multilayer photographic elements are well known in the art. Such materials generally have three different selectively sensitized silver halide emulsion layers coated on one side of a single support. Each layer has components useful for forming a particular color in an image. Typically, they utilize color forming couplers that form yellow, magenta and cyan dyes in the sensitized layers during processing.
After color development, it is necessary to remove the silver image that is formed coincident with the dye image. This can be done by oxidizing the silver using a suitable oxidizing agent, commonly referred to as a bleaching agent, in the presence of a halide, followed by dissolving the silver halide so formed using what is known as a fixing agent. In some instances, the bleaching and fixing steps are combined into a single bleach-fixing step.
A commercially important process intended for use with color reversal photographic elements that contain color couplers in the emulsion layers, or layers contiguous thereto, uses the following sequence of processing steps: first developing, washing, reversal bath, color developing, bleaching, fixing, washing and stabilizing.
In such photographic processes, a bleach-accelerator bath is often used between the color developing and bleaching steps. The bleach-accelerator bath is also known as a "conditioning" bath or solution. It is used to "condition" the metallic silver developed in the two developing steps, for complete oxidation to silver halide and to help preserve the acidity of the bleaching solution by reducing carryover of color developer into the bleaching solution. The conditioning solution contains, as an essential component, an effective amount of a bleach-accelerating agent. This agent is imbibed into the emulsion layers of the photographic element during treatment with the conditioning bath, and is accordingly present to exert its intended effect when the element is put into the bleaching solution.
Magenta dye instability is a particularly undesirable problem in color photography, as the magenta dye image may fade more rapidly than either the cyan or yellow dye images. This is particularly evident when arylpyrazolone type magenta dye forming color couplers are used. Thus, considerable effort has been exerted to find solutions to this problem, including the use of dye stabilizers in stabilization baths at the end of the processing method, as described in U.S. Pat. No. 4,786,583 (Schwartz).
It is also known from U.S. Pat. No. 4,921,779 (Cullinan et al), U.S. Pat. No. 4,975,356 (Cullinan et al) and U.S. Pat. No. 5,037,725 (Cullinan et al) that formaldehyde precursors can be incorporated into conditioning solutions to further improve magenta dye stability. These patents describe a number of formaldehyde precursors for this purpose including sodium formaldehyde bisulfite, hexamethylenetetramine and various methylol compounds.
U.S. Pat. No. 5,334,493 (Fujita et al) describes the use of a combination of formaldehyde and a secondary amine to allegedly stabilize magenta dyes in the processing of photographic elements. The combined materials can be included in any of a variety of processing solutions including "final" stabilizing solutions. It would be desirable, however, to avoid the use of formaldehyde entirely since it is an environmental and potentially health hazard.
For some time, conditioning solutions for color reversal film processing have been used which contain relatively high concentrations of sodium formaldehyde bisulfite (for example, over 40 g/l and as much as 55 g/l). This effectively solves the magenta dye instability problem but there is a growing concern about the potential health hazards from exposure to formaldehyde during photofinishing. Various governmental regulations are requiring less exposure to formaldehyde.
Thus, there is a need for a conditioning solution containing reduced amounts of formaldehyde precursor, but which still provides magenta dye stability.